1. Technical Field
The present invention relates to a method for manufacturing a semiconductor substrate and a method for manufacturing a semiconductor device, particularly to a technique, which forms a silicon on insulator (SOI) structure on a semiconductor substrate.
2. Related Art
In the method for manufacturing the semiconductor device, as described in ‘T.Sakai et al., “Second International SiGe Technology and Device Meeting, Meeting Abstract, pp. 230-231, May (2004)”’, a SOI layer is formed locally on a bulk silicon substrate, and a SOI transistor is formed on the SOI layer, using a method of separation by bonding Si islands (SBSI). The SOI transistor is formed at low cost by locally forming the SOI layer.
The method of forming the SOI structure on a bulk silicon substrate will be described with reference to FIG. 13. FIG. 13 is a schematic sectional drawing showing a part of a manufacturing method of a semiconductor substrate. When forming a SOI structure on a bulk silicon substrate 101, a local oxidation silicon (LOCOS) oxide film 104 may be formed on the bulk silicon substrate, in order to insulate the SOI structure region and the bulk structure region. Un-illustrated oxide film and nitride film formed on the bulk silicon substrate 101 are patterned, and the LOCOS oxide film 104 is formed in the desired location as shown in FIG. 13. Thereafter, after removing the nitride film, the oxide film on the SOI region 102 is removed, and a silicon germanium (SiGe) layer 105 and a silicon (Si) layer 106 are deposited on the bulk silicon substrate 101 by epitaxial growth. Consequently, on the bulk silicon substrate 101 in the SOI region 102, single-crystal silicon layers (an un-illustrated first silicon germanium layer and a first silicon layer 106a), in which a crystalline property of the bulk silicon substrate 101 is reflected, are formed. At the same time, polycrystalline silicon layers 112 (a second silicon germanium layer 105b and a second silicon layer 106b) are formed on the bulk silicon substrate 101 except for the SOI region 102.
Thereafter, a support hole 107a is formed which is for forming the support 107 so that the first silicon layer 106a is supported. An oxide film is deposited for making the support 107, and the circumjacent oxide film, a silicon layer 106, and a silicon germanium layer 105 are dry etched so as to obtain the shape of a device region (forming the support). The first silicon germanium layer under the first silicon layer 106a is then removed by a selective etching using fluoro-nitric acid, thereby forming a cavity beneath the first silicon layer 106a, supported by the support 107. A buried oxide (BOX) layer 108 is formed between the bulk silicon substrate 101 and the first silicon layer 106a, by burring an insulation layer with material such as SiO2. Thereafter, the SOI structure is formed on the SOI region 102 which is on the bulk silicon substrate 101, by planarizing the surface of the bulk silicon substrate 101 and exposing the first silicon layer 106a to the surface.
However, the second silicon germanium layer 105b, formed in the region except for the SOI region 102, is a cause of contamination, not being removed after the support and the BOX layer are formed, remaining exposed to the later processes. This includes the problem that, for instance, the interior atmosphere of a reactor for forming the semiconductor substrate includes germanium, and by the time the semiconductor substrate is completed, the germanium would be deposited on the films and the like of the semiconductor substrate, causing deterioration in the characteristics of transistors, such as a current leak.